1. Field of the Invention
The present invention relates to a timing signal generating circuit, a semiconductor integrated circuit device and semiconductor integrated circuit system to which the timing signal generating circuit is applied and a signal transmission system and, more particularly, to a timing signal generating circuit aimed at increasing the speed of signal transmission between LSI (Large Scale Integration Circuit) chips or between a plurality of devices or circuit blocks within one chip.
2. Description of the Related Art
Recently, the performance of components used in computers and other information processing apparatuses has improved rapidly; in particular, the performance of dynamic random access memories (DRAMs) and processors has improved dramatically year by year.
Namely, processor performance has increased dramatically in terms of speed, whereas DRAM performance improvements have been dramatic primarily in terms of storage capacity. However, the improvement in DRAM speed has not been so dramatic as the increase in storage capacity, as a result of which a gap between the speed of DRAMs and that of processors has widened and, in recent years, this speed gap has been becoming a bottleneck in boosting computer performance.
Further, with increasing chip size, not only signal transmission between the chips but also the speed of signal transmission between devices and between constituent circuits (circuit blocks) within one LSI chip (semiconductor integrated circuit device) is becoming a major limiting factor in chip performance.
On the other hand, if the speed of signal transmission between LSI chips is to be extremely increased, for example, it is required that signal receiving circuits be made to operate with correct timing to the signals, and techniques such as DLL (Delay Locked Loop) and PLL (Phase Locked Loop) have been known for addressing this requirement.
In addition, the need has arisen for high-speed signal transmission between LSI chips, for example, between a DRAM and a processor (logic circuit), or between a plurality of devices or circuit blocks within one LSI chip. There is, therefore, a need for a timing signal generating circuit that can generate with simple circuitry and with high accuracy a plurality of timing signals, having prescribed phase differences, synchronous with a reference clock.
Furthermore, with increasing operating speeds of LSIs, there is also a need for a signal transmission system that can perform large-capacity signal transmission at high speed between LSIs and between apparatuses constructed with a plurality of LSIs.
The prior art and the problems associated with the prior art will be described in detail later with reference to drawings.
An object of a first aspect of the present invention is to provide a semiconductor integrated circuit device that permits timing design with relatively high adjustment accuracy to be done in a short period. An object of a second aspect of the present invention is to provide a signal transmission system capable of high-speed, error-free signal transmission without being affected by skew on each signal line. An object of a third aspect of the present invention is to provide a timing signal generating circuit that can generate with simple circuitry and with high accuracy a plurality of timing signals, having prescribed phase differences, synchronous with a reference clock.
According to the present invention, there is provided a semiconductor integrated circuit device having a command decoder for issuing a control command in accordance with a supplied control signal, a DRAM core, and a timing adjusting circuit for supplying the control command, set active for a predetermined period, as a DRAM control signal to the DRAM core, wherein the timing adjusting circuit generates n different clocks that are respectively shifted in phase with respect to a supplied reference clock, and generates the DRAM control signal by setting the control command active in a prescribed operation cycle only for a period starting at a first predetermined clock pulse of a first clock of the n clocks and ending at a second predetermined clock pulse of a second clock of the n clocks.
The timing adjusting circuit may include a logic gate for enabling the generated DRAM control signal for output only for a period during which the control command is issued. The semiconductor integrated circuit device may include an MPU that accesses the DRAM. The timing adjusting circuit may include a first counter for counting the first clock; a second counter for counting the second clock; and a timing buffer circuit for generating the DRAM control signal by setting the control command active for a period starting from the time that the count value of the first counter reaches a first value and lasting until the time that the count value of the second counter reaches a second value.
The first counter and the second counter may be loop counters. At least, either one of the first and second counters may include a selection circuit for accepting multiple bit outputs from the counter, and for selecting one bit output out of the multiple bit outputs for output in accordance with a selection control input value; and a timing setting section for storing and outputting the selection control input value.
The timing setting section may be a register. The output of the timing setting section may be set before shipment in accordance with production process conditions. The output of the timing setting section may be set before shipment in accordance with required operating speed.
The timing adjusting circuit may include a common counter for counting one of the n clocks, or the reference clock, as a common clock; a first logic gate for enabling one of the n clocks for output only for a period during which the count value of the common counter shows a first value; a second logic gate for enabling one of the n clocks for output only for a period during which the count value of the common counter shows a second value; and a timing buffer circuit for generating the DRAM control signal by setting the control command active for a period starting from the time that the output of the first logic gate becomes active and lasting until the time that the output of the second logic gate becomes active.
The common counter may be a loop counter. The common counter may include a selection circuit for accepting multiple bit outputs from the counter, and for selecting one bit output out of the multiple bit outputs for output in accordance with a selection control input value; and a timing setting section for storing and outputting the selection control input value.
The semiconductor integrated circuit device may include a logic gate for supplying the common clock to the first counter only for a period during which the control command is issued. The command decoder may include a logic gate for enabling the first value indicated as the count value of the first counter for output to the timing buffer circuit only for the period during which the control command is issued.
The semiconductor integrated circuit device may include a selection circuit for selecting one of the n clocks in accordance with a selection control input value and for supplying the selected clock as a clock to the first logic gate or the second logic gate, and a timing setting section for storing and outputting the selection control input value. The timing setting section may be a register. The output of the timing setting section may be set before shipment in accordance with production process conditions. The output of the timing setting section may be set before shipment in accordance with required operating speed.
According to the present invention, there is also provided a timing adjusting circuit for generating n different clocks that are respectively shifted in phase with respect to a supplied reference clock, and for generating a control signal by being set in an active state in a prescribed operation cycle only for a period starting at a first predetermined clock pulse of a first clock of the n clocks and ending at a second predetermined clock pulse of a second clock of the n clocks.
Further, according to the present invention, there is provided a signal transmission system for transmitting and receiving signals using a plurality of signal lines, comprising a timing adjusting unit for adjusting the amount of signal delay caused during the transmission and reception of the signals in accordance with skew on each of the signal lines, thereby adjusting signal latch timing at a receiving circuit provided for each of the signal lines so that the latch timing becomes optimum for the signal line.
The timing adjusting unit may give, in effect, a variable delay to a clock used to drive each of the receiving circuits to latch each of the signals. The timing adjusting unit may include a phase interpolator that generates from a plurality of clocks with different phases a new clock having an intermediate phase. The timing adjusting unit may include a phase interpolator that generates from a plurality of clocks with different delay amounts a new clock having an intermediate delay amount. The timing adjusting unit may give, in effect, a variable delay to each of the signals at transmitting end.
The signal transmission system may further comprise a retiming circuit for retiming the plurality of signals latched at optimum timing from the plurality of signal lines so that all of the plurality of signals change synchronously with a common clock; and a deskew circuit for inserting, in the event of occurrence of a skew greater than or equal to a data cycle, a necessary amount of delay equivalent to an integral multiple of the data cycle.
The timing adjusting unit may include a plurality of latch circuits for latching the signals, and interleaving operations between two or more parts may be performed using the plurality of latch circuits. The plurality of latch circuits that perform the interleaving operations may be each constructed as a circuit employing a PRD method. The clock used to drive each of the receiving circuits to latch each of the signals may be derived from a signal on a dedicated clock line. The clock used to drive each of the receiving circuits to latch each of the signals may be generated internally, based on a phase comparison between a signal on a data line or a dedicated clock line and a reference clock internal to the receiving circuit.
The timing adjusting unit may include, at a receiving end, an optimum timing determining unit for determining an optimum point of the signal latch timing, and the optimum timing determining unit may determine the optimum point of the signal latch timing by using a first clock and a second clock having a predetermined phase difference with respect to the first clock.
The second clock may have a phase difference of approximately 180 degrees with respect to the first clock. The optimum timing determining unit may detect a data transient region by using the first clock and may determine the optimum point of the signal latch timing by using the second clock so that signal latching at the receiving circuit is achieved at optimum timing. The timing adjusting unit may include, at receiving end, an optimum timing determining unit for determining an optimum point of the signal latch timing, and the optimum timing determining unit may determine the optimum point of the signal latch timing by using a clock having a duty cycle of approximately 50%.
The optimum timing determining unit may detect a data transient region by using the clock and may determine the optimum point of the signal latch timing by using the complement of the clock so that signal latching at the receiving circuit is achieved at optimum timing. The timing adjusting unit may include, at transmitting end, an optimum timing determining unit for determining an optimum point of the signal latch timing, and the optimum timing determining unit may transmit data at such timing that a clock, at receiving end, occurs at an optimum point of data.
The optimum timing determining unit may include a calibration mode for transmitting data at first timing and a data transmission mode for transmitting data at timing shifted by a predetermined phase difference with respect to the first timing, and wherein the calibration mode may detect a transient region in the data of the first timing by using the clock at the receiving end, and the data transmission mode may ensure that the data of the timing shifted by the predetermined phase difference with respect to the first timing is latched by the receiving circuit by using the clock at the receiving end. The timing shifted by the predetermined phase difference with respect to the first timing may be timing having a phase difference of approximately 180 degrees with respect to the first timing.
The signal transmission system may further comprise a phase information extracting unit for extracting phase information of a clock on a clock line or a data line; and a storing unit for sending the phase information of the clock to each of the receiving circuits, and for storing for each of the receiving circuits a relative phase value representing the phase difference between the optimum receiving timing required at each of the receiving circuits and the clock actually used and wherein, when performing the signal latching, the optimum receiving timing at each of the receiving circuits is determined by taking a sum of the phase information of the clock and the stored relative phase value for each of the receiving circuits.
The timing adjusting unit may include, at receiving end, a delay circuit for delaying data. The delay circuit may be constructed as a variable delay circuit capable of delaying an analog signal.
Further, according to the present invention, there is also provided a timing signal generating circuit comprising a master circuit for generating by feedback control an internal signal having the same cycle or the same phase as that of an input reference signal; and a slave circuit for generating a timing signal having a prescribed timing relative to the reference signal by receiving the internal signal and a control signal from the master circuit.
A plurality of slave circuits may be provided for one master circuit. The master circuit may contain a circuit corresponding to the slave circuit so that the master circuit may also output a timing signal by itself.
The master circuit may comprise a comparator circuit for comparing the cycle or phase of the internal signal with that of the reference signal, a control signal generating circuit for varying the control signal in accordance with an output of the comparator circuit, and a variable delay line for outputting the internal signal by controlling a delay amount for the reference signal in accordance with the control signal.
The master circuit may be a DLL circuit which comprises a coarse delay control block for performing coarse delay control and a fine delay control block for performing fine delay control, and the slave circuit contains a circuit corresponding to the fine delay control block. The coarse delay control block may take taps off the delay line consisting of a plurality of delay units, and may perform coarse delay control by selecting an output of each of the taps, while the fine delay control block receives a signal for controlling the DLL circuit in the coarse delay control block and a signal subjected to the coarse delay control in the coarse delay control block, and performs fine delay control through an interpolator by using the coarse delay control signal.
The control signal generating circuit may include a charge pump circuit for controlling an output voltage level in accordance with an up signal and a down signal from the comparator circuit. The control signal generating circuit may include an up-down counter for counting an up signal and down signal from the comparator circuit and a D/A converter for performing digital-to-analog conversion on an output of the up-down counter.
The master circuit may comprise a comparator circuit for comparing the cycle or phase of the internal signal with that of the reference signal, a control signal generating circuit for varying the control signal in accordance with an output of the comparator circuit, and a voltage-controlled oscillator for generating an internal signal corresponding to the reference signal in accordance with the control signal.
The slave circuit may include a voltage-controlled oscillator for outputting the timing signal in accordance with the control signal from the master circuit. The control signal generating circuit may include a charge pump circuit for controlling an output voltage level in accordance with an up signal and down signal from the comparator circuit. The control signal generating circuit may include an up-down counter for counting an up signal and a down signal from the comparator circuit and a D/A converter for performing digital-to-analog conversion on an output of the up-down counter.
The slave circuit may include a variable delay line for outputting the timing signal by delaying the internal signal in accordance with the control signal from the master circuit. The slave circuit may include a phase interpolator for accepting input signals of different phases and for outputting a finer timing signal of an intermediate phase.
The input signals of different phases may be three-phase or four-phase clocks. The phase interpolator may include a voltage-to-current converting unit for converting a plurality of input voltage signals respectively to current signals, a current-to-voltage converting unit for converting the converted current signals back to voltage signals by varying voltage conversion factors, and a comparing unit for comparing a sum of the converted current signals with the reference signal.
The control signal sent from the master circuit to the slave circuit may be a control current signal. A control current signal generating circuit for generating the control current signal may be provided in the master circuit, and a current-to-voltage conversion circuit for converting the control current signal to a voltage signal may be provided in the slave circuit. The slave circuit may include an amplifier circuit whose response speed varies in accordance with a signal from the master circuit, and may generate a signal of sinusoidal waveform as the timing signal.
The slave circuit may be used to generate a timing signal for controlling the timing of one-bit or multiple-bit input or output signals, and the timing signal generating circuit may include timing signal adjusting unit, provided common to each of the slave circuits, for adjusting the timing signal so as to increase the S/N ratio of a transmitted and received signal. The timing signal adjusting unit may include a selecting unit for selecting an input or output signal of a circuit controlled by the timing signal from each slave circuit, and a timing signal generating unit for controlling output timing of the timing signal by detecting the level of the input or output signal of the circuit selected by the selecting unit.
The slave circuit may be used to generate a timing signal for controlling the timing of one-bit or multiple-bit input or output signals, and each of the slave circuits may include a timing signal adjusting unit for adjusting the timing signal so as to increase the S/N ratio of a transmitted and received signal.
In addition, according to the present invention, there is provided a semiconductor integrated circuit device employing a timing signal generating circuit comprising a master circuit and at least one slave circuit, the master circuit and the slave circuit being formed on the same semiconductor chip used for the semiconductor integrated circuit device, wherein the master circuit generates an internal signal having the same cycle or the same phase as that of an input reference signal by feedback control; and the slave circuit generates a timing signal having prescribed timing relative to the reference signal by receiving the internal signal and a control signal from the master circuit.
Furthermore, according to the present invention, there is also provided a semiconductor integrated circuit system employing a timing signal generating circuit comprising a master circuit and at least one slave circuit, the semiconductor integrated circuit system having a plurality of semiconductor integrated circuit devices, each of the semiconductor integrated circuit devices having the master circuit and/or the slave circuit and being formed on corresponding one semiconductor chip, wherein the master circuit generates an internal signal having the same cycle or the same phase as that of an input reference signal by feedback control; and the slave circuit generates a timing signal having prescribed timing relative to the reference signal by receiving the internal signal and a control signal from the master circuit.
According to the present invention, there is provided a phase interpolator comprising an analog periodic waveform generating unit for generating an analog periodic waveform, whose value varies in an analog fashion, from a digital periodic signal whose amplitude represents a digital value; a summed waveform generating unit for generating a summed waveform by summing a plurality of analog periodic waveforms obtained by the analog periodic waveform generating unit from digital periodic signals displaced along time axis; a weighting control unit for controlling the weighting of each of the analog periodic waveforms; and an analog/digital converting unit for converting the summed waveform to a digital waveform.
The analog periodic waveform generating unit may include a sine wave generating circuit, and the weighting control unit may include a plurality of transfer gates connected in parallel and controlled for connection. Each transfer gate in the weighting control unit may have a transistor of the same size, and the weighting of the analog periodic waveform may be controlled by controlling the number of transfer gates caused to conduct. Each transfer gate in the weighting control unit may have a transistor of a different size, and the weighting of the analog periodic waveform may be controlled by causing at least one transfer gate having a transistor of a prescribed size to conduct.
The analog periodic waveform generating unit may include a plurality of CMOS inverters, and the weighting control unit may control the number of CMOS inverters to be connected. The analog periodic waveform generating unit may include a plurality of CMOS inverter output stages, and the weighting control unit may control the number of output transistors forming the plurality of CMOS inverter output stages.
The analog periodic waveform generating unit may be a high-frequency attenuation circuit for attenuating high-frequency components of the digital periodic signal, and the weighting control unit may convert an output of the high-frequency attenuation circuit into a current by means of a variable transconductor and apply the converted current to a common terminal. The analog periodic waveform generating unit may be an integrator circuit. The analog periodic waveform generating unit and the summed waveform generating unit may comprise a current polarity switching unit for switching the polarity of a current flowing from a constant current source to a common capacitive load by the digital periodic signal; and a current value control unit for controlling a current value of the current source.
The current value control unit may control the current value of the current source by an output of a D/A converter. The analog/digital converting unit may be a comparator for comparing the summed waveform with a reference level for conversion into a digital waveform. The weighting control unit may include a current-output D/A converter, and an output of the D/A converter may be controlled by being switched for connection to either a capacitive-coupled terminal or its complementary terminal.
The weighting control unit may be configured to vary the number of current sources to be connected to a load capacitance terminal. The weighting control unit may include a clamp circuit for holding a terminal voltage level within a fixed range. The phase interpolator may be configured so that the size of transistors to be switched and the quantization step size of a D/A converter are made variable to provide a desired linearity characteristic to a timing output versus a control signal.